\(\sqrt{\frac{1}{N}\sum\limits_{1}^{N} \left(\overline{f} - o\right)^{2}}\)
\(\sqrt{\frac{1}{N}\sum\limits_{1}^{N} \left(Var\left(f\right)\right)}\)
\(\sqrt{\frac{1}{NM-1}\sum\limits_{i=1}^{NM} \left(f_{i} - o\right)^{2}}\)
\(\sqrt{\frac{1}{N}\sum\limits_{1}^{N} \left(Var\left(f\right)\right)}\)